1. Field of the Invention
The present invention relates to rigging, namely slings and grommets that are used during heavy lifting and more particularly to a heavy lifting system that includes a specially configured sling and grommet of improved construction wherein an elongated sling member includes an elongated woven portion having first and second ends and a central passageway surrounded by the woven material, and wherein one or more flexible sleeves can be optionally fitted to the elongated sling member at its loop portions and at its connecting portions. If the tensile material is one large circular loop, it is referred to as a grommet. These elongated sleeves are preferably of a spiral construction that can be easily installed in the field once a sling length is selected, and function to prevent abrasion during use and to prevent slippage at the splice. The grommet has a similar flexible sleeve fitted to splices of the grommet.
2. General Background of the Invention
In the lifting of very heavy items, lifting harnesses are typically employed which comprise an elongated length of tensile material having loops at each end. These slings have commonly taken the form of wire rope having looped ends. In the case of wire rope, the looped ends are often secured using a crimp or band. Once the sling is constructed, its length is “fixed”. A user must plan the lift in advance by selecting slings of a desired fixed length.
Polymeric and plastic material has been used to construct slings and grommets. A grommet is a sling that is circular in shape so that the user simply hooks or grabs the entire sling rather than a looped end portion. New England Ropes publishes a “Splicing Guide” that discloses various rope splicing techniques.
One of the problems with slings and grommets of either metallic or plastic construction is that of field adjusting the sling length. Wire rope slings are not adjustable. Plastic and polymeric slings are typically sewn to form the loops so that they are not easily adjustable on the job site.
One polymeric material that has a high tensile strength is liquid crystal polymer fiber. One brand that is manufactured by Celanese Acetate LLC is sold under the trademark Vectran®. Celanese literature states that Celanese has contracted aerospace and rope manufacturers to conduct pin diameter tests on Vectran® braid and wire rope respectively. The same literature shows a braid test using a braid having two eyes at the ends. However, this type of “test” braid would quickly become disassembled and or slip in routine use as a sling in a construction environment.
When rigging for many different lifts during a day, a rigger desirably wants a sling that is adjustable so that the length can be varied to fit the particular item being lifted. Further, slings should not slip or become disassembled on the job.